Ah, your talking about Alex Mercer. I've played this game and it was awesome to play. My most favourite thing to do on this game was take over a tank and blow up those annoying solider's bases for revenge.
As you progress further through the game the story gets intense and so do the soliders themselves, it becomes harder and harder to hide from them and most of the time you end up getting killed because the helicopters are just hard to lose.
The only way I could lose a helicopter was find a bridge to hide under that a helicopter couldn't fly under or fly close to, there is one in the city where it's surrounded by buildings and has a part in the bridge created for people to walk under. The perfect hiding space since when you hide here the helicopters can't find you, you can shape shift into another person or wait out the alert.